1. Field of the Invention
This invention relates to an image-forming apparatus having a cleaning blade kept in contact with an image-carrying member such as an amorphous-silicon photosensitive member, and also relates to the cleaning blade.
2. Related Background Art
Nowadays, as image-forming apparatus of an electrophotographic system, complex machines having all output terminals such as a copying machine, a printer and a facsimile machine together have come to be accepted in the market. This means that electrophotographic systems have widely been accepted as output terminals adaptable to such a network. However, as one of great problems, the xe2x80x9cduty cyclexe2x80x9d has become a subject of discussion. The duty cycle herein refers to the limit number of sheets for which the main body continues being normally operated without any serviceman maintenance. One of the most important factors which determine the duty cycle is considered to be the lifetime of photosensitive drums.
From the viewpoint of ecology, it has also become absolute subjects for manufacturers to lessen any waste, i.e., to lessen any articles for consumption, make such articles for consumption have a longer lifetime and improve their reliability.
Moreover, with progression from conventional analog apparatus to digitized ones, it has also become absolute subjects to make the main-body cost equivalent to, or lower than, that of analog ones.
Furthermore, in recent years, in copying machines and printers, which have hitherto chiefly been held by black-and-white machines, originals or output files are rapidly increasingly being made full-color also in offices. Not only digital machines equivalent to analog machines but also full-color printers equivalent to black-and-white machines in respect of main-body cost and running cost have become absolute subjects. In order to settle such subjects, techniques which can dramatically lower TCO (total cost of ownership; total necessary cost viewed from users) are desired.
Under such circumstances, amorphous-silicon photosensitive members have become more and more widely used because of their high hardness (9,800 N/m2 or more in Vickers hardness) and superior durability (running performance), heat resistance and environmental stability, and have become indispensable for high-speed machines which are required to have especially high reliability. The amorphous-silicon photosensitive members have replacement lifetime in a number of sheets which is at least one digit larger than OPC (organic photoconductor) photosensitive members commonly used in recent years. In other words, they have a lifetime equivalent to the main-body lifetime, and also have the effect on waste reduction. In addition, they do not take time and labor for, e.g., collection and regeneration of process cartridges making use of the OPC photosensitive members.
If the techniques making use of such amorphous-silicon photosensitive members mounted on high-speed machines come mountable on full-color printers, it is considered achievable to provide apparatus which can achieve the duty cycle and low running cost of the high-speed machine in respect of black-and-white printing and also can perform color printing. In particular, in order to achieve the duty cycle and low running cost of high-speed machines on the part of users who use black-and-white printing in a high percentage, it is considered essential to mount the amorphous-silicon photosensitive member on a one-drum type full-color printer making use of a rotary developing assembly.
However, in the apparatus of this type, the stuff adhering to the photosensitive-member (image-bearing member) surface to affect image quality are not only the toner. Any foreign matter having adhered to the photosensitive-member surface, such as fine paper dust coming from paper used as transfer materials in almost all cases, organic components depositing therefrom and corona products produced because of the presence of a high-pressure member in the apparatus, may cause low-resistance especially in a high-humidity environment to obstruct the formation of sharp electrostatic latent images. This is considered to be the factor which causes deterioration in image quality. Such a phenomenon of the deterioration in image quality is known to tend to occur in the case of the amorphous-silicon photosensitive member, which is constructed by forming films by glow discharge decomposition of silanes.
In order to avoid such a disadvantage, especially when one-component magnetic toners are used, a cleaning assembly is proposed in which a magnet roller is provided on the upstream side of a cleaning blade as viewed in the travel direction of the photosensitive member, to form a magnetic brush with part of the toner collected into the cleaning assembly, and this magnetic brush is brought into contact with the photosensitive-member surface to re-supply the magnetic toner thereto so that the foreign matter like the above can be removed by rubbing by the abrasive action attributable to toner particles at the blade portion.
In the means making use of such a magnetic brush, the abrasive action may hardly be localized non-uniformly on the photosensitive-member surface and may cause less deterioration of the photosensitive member, than the manner in which the photosensitive-member surface is rubbed with an abrasive member prepared separately such as a web or a rubber roller. In combination with such a method, an additional means may be used in which, e.g., the photosensitive member is provided with a heater so that its surrounding humidity can be kept low during night and stand-by to prevent the photosensitive-member surface from becoming low-resistance. This has achieved a certain effect to hold back image deterioration to be caused as stated above.
In image-forming apparatus which repeats the step of transferring transferable toner images formed on the photosensitive-member surface, to transfer materials chiefly comprised of paper, it is essential that residual toner remaining on the photosensitive member without being transferred to the transfer material at the timer of transfer is well removed each time.
Accordingly, as cleaning means, many proposals have been made up to now. Those in which the residual toner is scraped off by a cleaning blade comprised of an elastic materials such as urethane rubber are widely put into practical use because they are simple in construction, compact and low-cost and yet have good toner removal function. As a rubber material for the cleaning blade, urethane rubber is commonly used, as having a high hardness and yet being rich in elasticity, and excelling in wear resistance, mechanical strength, oil resistance and ozone resistance.
However, such a cleaning blade may cause filming on the photosensitive-member surface. The cause thereof is considered as follows: The photosensitive member has surface resistance which tends to become low-resistance. As factors which cause the photosensitive-member surface to have low resistance, fine paper dust coming from paper used as transfer materials in almost all cases, organic components depositing therefrom and various metal oxides and oxygen compounds produced at the time of high-energy corona discharge from a high-pressure member in the apparatus, together with any components becoming nitrate ions upon oxidation of nitrogen in air, may adhere to the photosensitive-member surface, so that a thin film (hereinafter xe2x80x9cfilming layerxe2x80x9d) is formed on the photosensitive-member surface as a result of long-term use.
Where a magnetic toner is used as a toner to perform magnetic brush development, the filming layer may readily be removed by the abrasive action of the toner particles at the cleaning blade. However, in the case of non-magnetic toners such as color toners, the toner particles have less abrasive action to tend to cause the filming layer. The filming layer may absorb moisture in a high-humidity environment to become low-resistance to obstruct the formation of sharp electrostatic latent images, and this may cause deterioration in image quality to cause, e.g., smeared images.
In order to remove the filming layer formed upon long-term use, the ability to rub the photosensitive-member surface must be improved. However, where, e.g., as a rubbing means an elastic roller is made to rub the photosensitive-member surface by bringing the former into contact with the latter at a peripheral speed made different from each other, the toner may locally adhere to the photosensitive-member surface. As the result, the toner may locally melt-adhere to the elastic roller surface, and the photosensitive-member surface may be abraded at the part corresponding thereto, resulting in uneven abrasion to cause faulty images.
If the photosensitive-member surface is made more highly abradable with the elastic roller in order to avoid the above problem, even the amorphous-silicon photosensitive member may wear in a large quantity to lower its reliability. Also, with such setting, the elastic roller itself also may wear in a large quantity to lower its reliability.
According to experiment made by the present inventor by an optical method, it has been ascertained that the filming layer due to long-term use is in a layer thickness of approximately from 3 to 8 nm. Its measurement with a reflection spectro-interferometer (manufactured by Otsuka Denshi K.K.; trade name: MCDP2000) at the initial stage of continuous use has also ascertained a filming layer. Then, it has been found that this filming layer reaches the layer thickness of from 3 to 8 nm, and after that the layer thickness little changes, but any image deterioration which had been eliminable at the initial stage by dry wiping, wet wiping or alcohol wiping becomes not eliminable as the photosensitive member is used for a longer term.
It has been found that the drum (photosensitive member) surface having reached such a state as a result of long-term use and with repetition of melt adhesion and wear must be polished with abrasive grains before the image deterioration can be eliminated; abrasive grains being those of cerium oxide (CeO2) of approximately from 0.3 xcexcm to 2 xcexcm in diameter dispersed in alcohol or the like. This tends to remarkably occur especially when a drum heater is not fitted.
In addition, the present inventor has put forward extensive studies and has examined photosensitive-member surfaces having various surface shapes by measuring their surfaces at the initial stage and after long-term use, with an AFM (atomic force microscope; manufactured by Digital Instruments Co.; trade name: ManoScope IIIa Dimension 3000; scanning mode: tapping mode; scanning range: 20 xcexcmxc3x9720 xcexcm; probe: silicon cantilever). As the result, it has been found that the photosensitive-member surfaces after long-term use have become almost smooth because of wear, compared with those at the initial stage. Also, as a result of heating (at 70xc2x0 C. to 80xc2x0 C. for 30 minutes) the photosensitive-member surfaces after long-term use, in an aqueous 5% sodium peroxodisulfate (Na2S2O8) solution, followed by ultrasonic cleaning (for about 1 minute) in acetone and then rinsing with an ethanol/pure water mixed solvent, it has been found that the level of filming is large especially at dales of unevenness of the photosensitive-member surface.
The filming may also result in an increase in frictional force. An experiment made by the present inventor has revealed that the frictional force acting between the transfer residual toner and the drum surface through the cleaning blade may increase because of the long-term use. This is considered due to the fact that the filming layer formed in the long-term use makes higher the adhesion and affinity between the cleaning blade and the drum surface and between the transfer residual toner and the drum surface to increase the frictional force acting between the transfer residual toner and the drum surface.
The increase in frictional force is considered due to an increase in shear stress of the cleaning blade, shear stress between toner particles and shear stress in the vicinity of the drum surface. As a result of the increase in these, the cleaning blade may chip (its edge may chip locally), heat may be generated in a large amount because of an increase in compression set shear stress to cause melt adhesion of toner, or fatigue wear may increase because of an increase in stress inside the drum, as so considered.
The melt adhesion of toner may also occur with a lapse of continuous operating time. In recent years, as stated previously, image-forming apparatus are not only used to function as copying machines but also used widely as printers. Also, with progress in the enrichment of auxiliary functions such as a feeder function and a sorter function, it has become possible to perform continuous operation on 4,000 sheets or more at one job. For example, in the case of a type of machine which can process 50 sheets of A4-sized paper in one minute, it follows that the continuous operation is performed for 80 minutes or more even in simple estimation. Under such circumstances, the atmospheric temperature reaches almost 50xc2x0 C. in the vicinity of the photosensitive member, and is considered to have reached a temperature higher than that at the contact part (nip) between the cleaning blade and the photosensitive member. Hence, the melt adhesion of toner to the photosensitive-member surface is considered to occur highly frequently.
Where two-component developers are used, there is also such a problem that any suitable preventive means can not be taken. Toners for full-color image formation are commonly non-magnetic materials. Conventionally, where the magnetic brush cleaning having been widely used in black-and-white machines is applied to full-color printers, a magnetic carrier must be kept held previously in a cleaner unit. This may result in insufficient reliability and durability (running performance).
The present invention was made in order to cope with the problems stated above. Accordingly, an object of the present invention is to provide an image-forming apparatus which can maintain the surface state of a photosensitive member that does not cause any smeared images or melt adhesion of toner even when non-magnetic toners are used, promising a great improvement in reliability, and also can deal with any situations even where the productivity has dramatically been advanced.
Another object of the present invention is to provide a cleaning blade useful for such an image-forming apparatus.
To achieve the above objects, the present invention provides an image-forming apparatus comprising a cleaning means provided with at least a cleaning blade, and an image-bearing member to be cleaned by the cleaning member, wherein;
the cleaning blade comprises an edge portion which is brought into contact with the image-bearing member, and a support portion which brings the edge portion into contact with the image-bearing member;
the value at a peak temperature (t1) of a loss tangent of the edge portion, tan xcex41, is smaller than the value at a peak temperature (t2) of a loss tangent of the support portion, tan xcex42; and
a curve which represents the temperature dependence of the loss tangent of the edge portion and a curve which represents the temperature dependence of the loss tangent of the support portion intersect at t1xc2x0 C. or above to t1+40xc2x0 C. or below.
When the loss tangent of the edge portion of the cleaning blade and the loss tangent of the support portion satisfy the above relationship, the edge portion behaves always stably against the photosensitive-member surface and the residual toner on the photosensitive-member surface. As a result, the lower-limit pressure at which the residual toner slips through can be set low, so that the melt adhesion of toner to the photosensitive-member surface can be reduced and the filming can be kept from occurring.
The temperature dependence of the loss tangent of the edge portion may be measured with a viscoelastometer (e.g., one manufactured by Rheometrix Co.; trade name: RSA2) at 10 Hz on a sample obtained by cutting out only the edge portion of the cleaning blade. The temperature dependence of the loss tangent of the support portion may also be measured with a viscoelastometer (e.g., one manufactured by Rheometrix Co.; trade name: RSA2) at 10 Hz on a sample obtained by cutting out only the support portion of the cleaning blade.
The image-forming apparatus of the present invention is an image-forming apparatus of an electrophotographic system, having a photosensitive member, a charging means, an exposure means, a developing means, a transfer means and a cleaning means, in which as a developer used is a developer containing at least non-magnetic toner particles and a magnetic carrier or a developer containing at least a magnetic toner. In this image-forming apparatus, the cleaning means cleaning blade is a cleaning blade having a cured layer formed at its edge portion (its edge and the vicinity thereof) which comes into contact with the image-bearing member, by impregnating that portion with an isocyanate compound followed by curing, and the behavior concerning loss tangents, the thickness of the impregnation-treated portion, the level of wear and so forth are controlled. Thus, it can maintain the surface state of a photosensitive member that does not cause any smeared images or melt adhesion of toner even when non-magnetic toners are used, promising a great improvement in reliability, and also can deal with any situations even where the productivity has dramatically been advanced.
In the case of an image-bearing member which has a high surface hardness, may abrade with difficulty and may wear at a small level, the melt adhesion of toner and the filming are liable to occur. However, the use of the cleaning blade having the characteristics as described above can keep the melt adhesion of toner and the filming from occurring.
The image-forming apparatus of the present invention may also be so constructed as to have a plurality of developing means in addition to the above construction so that full-color images can also be formed.